1. Field of the Invention
This invention relates to phase shifters and in particular to phase shifters whose shifting characteristics may be controlled.
2. Description of the Prior Art
One known type of phase shifter takes the form of an integrator circuit comprising an operational amplifier having a capacitor connected in series between its output and inverting input ports and a resistor connected between an input terminal and the inverting input port. With an ideal operational amplifier (i.e. one with infinite gain and infinite input impedance), this type of phase shifter provides, at all frequencies, exactly ninety degrees of phase shift between the input terminal and the output port. Although commercially available operational amplifiers do not have these ideal characteristics, they do exhibit characteristics which result in substantially ninety degree phase shifts over relatively wide frequency ranges.